1. Field of the Invention
The present invention relates to image display devices that display color images, and more particularly relates to color-image displaying image display devices that control after-images in motion pictures.
2. Description of the Background Art
Conventionally, images are displayed on screens by using projectors which employ ultra high pressure mercury lamps. However, such conventional projectors have a relatively short life span, and have been prohibitive of realizing instant switch-on. In addition, the conventional projectors have insufficient luminance, and in most cases, due to the influence of such factors as the room lighting or the screen, have been prohibitive of representing, for example, a prepared chart with the colors visually recognizable as on the computer screen. Thus, to solve this problem, in recent years image display devices that are equipped with solid-state light sources such as light emitting diodes (LEDs) and laser diodes (LDs), in place of the conventional ultra high pressure mercury lamps, have been proposed.
In order to display color images, a conventional image display device is equipped with solid-state light sources which emit light having wavelengths of three primary colors (red (hereinafter referred to as “R”), green (hereinafter referred to as “G”), and blue (hereinafter referred to as “B”)) and a modulator that is used in common for each of the solid-state light sources. The conventional image display device adopts a field sequential system which renders color images by high-speed flickering of the light from the solid-state light sources, and by controlling the modulator which modulates, in accordance with the flickering time, the light corresponding to the respective colors (e.g., see Japanese Laid-Open Patent Publication No. 2008-20600).
The conventional field sequential system has an R display period, a G display period, and a B Display period, which occur in order. In the R display period, only R-LEDs, which emit light having R wavelengths are lit, whereas the remaining light sources are turned off, and the modulator modulates only the R light. Accordingly, an R image is displayed. In the same manner, to display a G image and a B image, G-LEDs, which emit light having G wavelengths, and B-LEDs, which emits light having B wavelengths, are lit. The modulator then modulates the G light and the B light, respectively.
Another conventional image display device adopts a digital micromirror device (DMD, registered trademark of Texas Instruments Incorporated) as a modulator (e.g., see U.S. Pat. No. 5,969,710, and U.S. Pat. No. 6,778,155). This device employs a technique of bit splitting, in which during each of the R display period, the G display period, and the B display period, the DMD uniformly distributes within each period the time during which it reflects light from each light source, so as to reduce nonuniformity in light reflection time, thereby smoothing the luminance.
However, unlike impulse type display devices such as cathode-ray tubes, conventional hold-type display devices, such as DMD-employing image display devices and liquid crystal displays, cause a problem of generating image blur (motion blur) depending on the movement speeds of objects in moving images.
In order to reduce motion blur that arises in accordance with the moving speed of an object in a moving image, a technique of inserting a black signal synchronized to a vertical synchronization signal, as well as a technique of turning off the light that illuminates the display device have been disclosed. However, according to the conventional techniques, the black periods are distributed and the black period time span is short, and thus it has not been possible to reduce the motion blur sufficiently.